Heat exchanger

ABSTRACT

646,855. Descaling tubes. AMERICAN LOCOMOTIVE CO. Feb. 26, 1948, No. 5815. Convention date, Sept. 26, 1945. [Class 99 (ii)] In a heat-exchanger, wherein a least one end of the structure 7 is free to float longitudinally due to therma expansion and contraction of the tubes 8, and angularly-disposed tie rods 47, secured to the ends and en gaging at the central portion of the structure and which tend to straighten during expansion of the tubes, limit the outward movement of the structure whereby forced bowing and descaling of the tubes is effected bar means, such as two parallel members 59, are provided which space the structure ends in their normal positions and check the inward movement of the structure to ensure that the tubes, upon contraction, unbow to their normal positions. The members may comprise a tube 60 equal in length to the distance between the tube plates 11, 15, attached to plate 15 and telescoped within a tube 61 secured to plate 11. There may be a tie 62 between the members and a post 63 supporting the lower member. The tubes 8 may be in two groups 9, 10 each group passing through semi-circular plates 27 that may engage the tie-rods and which move laterally outwards during bowing of the tubes. U.S.A. Specification 1,855,552 is referred to.

8,1951 G. B. FARKAS 7 2,552,416

HEAT EXCHANGER 3 Sheets-Sheet l G. B. FA R KA 5 HEAT EXCHANGER May 8, 1951 3 Sheets-Sheet 2 Filed Sept. 26, 1945 I INVENTOR George .B. Fq fl 54 BY KG W ATTOR Y G. FARKAS HEAT EXCHANGER May 8, 1951 3 Sheets-Sheet 3 Filed Sept. 26 1945 ndvnnon George B Farkas Patented May 8, 11951 UNITED STATES ATENT OFFICE HEAT EXCHANGER George B. Farkas, Jackson Heights, N. Y.', assignor to American Locomotive Company, New York, N. Y., a corporation of New York Application September 26, 1945, Serial No. 618,623

7 Claims. (01. 257239) 2 J. This invention relates to heat exchangers and VIII-VIII of Fig. 6 showing the tie rods in more particularly to a structure including a bunstraightened out position and the plate shoulders die f h e n e tubes and end tube sheets contiguous thereto; Fig. 9 is a section on the line and headers for the tubes, and a control for the VIII-VIII of Fig. 6 showing the tie rods in structure for effecting descaling of the tubes. straightened-out position but with the plates This invention is an improvement of the inmoved laterally therefrom upon the application vention disclosed in the patent to Jacocks et al., of additional heat to the tubes; and Fig. 10 is a No. 1,855,552, dated April 26, 1932, wherein de detail view showing the stop means in extended scaling of tubes is effected by bowing and unposition.

bowing the tubes to flake ofi scale deposits in The present invention, for illustrative purposes,

thereon. is shown in connection with a shell type of heat According to the invention of the aforesaid exchanger and will be so described, but it may patent, means for positively causing bowing of be used with other types of heat exchangers, as the tubes is provided. However, means for infor instance with the cooling tower shown in the suring unbo'wing of the tubes is not provided. if aforesaid Jaco as et a1. patent. It has been .This presents various disadvantages. It prevents stated that the present invention is an improvemaximum bowing and unbowing of the tubes and mom; of the heat exchanger of the J acocks et al. therefore decreases the efficiency of the descaling patent. Therefore various features will be briefly operation. Furthermore it results in increasing described and reference may be had to the J acocks the cross-sectional area of the tube bundle when It, et a1. patent for a fuller understanding thereof. the tubes do not unbow to their original condi- The invention, for convenience, is illustrated in tion, which may prevent the withdrawal of the connection with a shell type of heat exchanger. structure through an opening provided in the The shell, which is horizontally disposed, is indiheat exchanger shell where the structure is em cated by the reference numeral I. It is supported ployed in a shell type of exchanger, the with by legs 2, has a water inlet 3, a steam outlet 4, drawal being periodically necessary for the pur drains 5 and an outwardly flanged opening 6 at pose of cleaning and repairing the parts. the front.

The object of the present invention is to insure The structure of the present invention is indithe tubes of the bundle assuming their original cated generally by the reference numeral 7 and position and having maximum unbowing during :m includes a bundle of fluid conducting tubes 8 ver contraction so that there will be no increase in tically divided into two groups 9 and It. The cross-sectional area of the bundle at final contubes are secured at their rear ends in a tube traction of the tubes and so that maximum bowsheet I I covered by a header or cap l2, the tubeing and unbowing may be effected during thermal sheet and header being secured together by a expansion and contraction of the tubes. split clamp ring [3 of usual construction, the

Referring to the drawings forming a part of clamp being provided with the usual set screws l4. this application, Figure 1 is an elevation in par- The tubes are secured at their forward ends tial vertical central section on the line II of Fig. in tube sheet 55 which is covered by a header 2, of a shell type heat exchanger embodying the or channel It. The channel at its rear end is outpresent invention; Fig. 2 is a section on the line 40 wardly flanged and is secured to the flange of IIII of Fig. 1, parts being broken away and the opening 6, with the tube sheet l5 interposed, other parts being shown in full; Fig. 3 is an enby another clamp ring is having set screws 44'. larged section on the line IIIIII of Fig. 2, apart The channel is outwardly flanged at its forward being shown in dot and dash lines; Fig. 4 is a end and covered by a plate ll, the plate being foreshortened section on the line IV-IV of Fig. secured to the forward flange by another clamp 3, parts being broken away and parts being shown ring 13 having set screws M. The channel in full; Fig. 5 is an enlarged detail shown fragis divided interiorly by a horizontal partition l8 mentally and partly in section; Fig. 6 is a view, into a large upper compartment [9 which comsimilar to Fig. 2, showing the tube bundle bowed, mum'oates with and supplies steam to most of the tie rods straightened out, and the associated so the tubes and has a steam inlet 20, and a relaelements moved to changed position when the aptively small lower compartment 2! which comparatus has been heated in normal operation; Fig. municates with the remaining relatively small 7 is a section on the line VII-VII of Fig. 2 shownumber of tubes, and which is provided with an ing the apparatus in original or room ternperaoutlet 22.

ture position; Fig. 8 is a section on the line The steam travels through the upper tubes in the direction of the arrows from the compartment E9 to the header l2, and from the header [2 through the small number of tubes at the bottom to the compartment 2|. It will be understood that the various outlets and inlets before mentioned are flanged for connection with suitable piping in the usual manner.

The structure I, and the control for the expansion and contraction of the tubes which will later be described, form a unit which is secured at its front end portion to the front end of the shell by the clamp ring l3 in the manner aforesaid. Except for this connection and the pipe connections (not shown) for the steam inlet 29 and outlet 22, the unit is otherwise free and therefore floats at its rear end.

The structure is removable from the shell by merely removing the clamp ring l3 and the aforesaid pipe connections. This frees the channel for removal and leaves the remainder of the structure and the control free for removal from the shell, the control and structure parts to the rear of the tube sheet I5 being free for withdrawal through the opening 6 in the shell for repair and cleaning.

Where the invention is used in connection with a shell type of heat exchanger, as in the present instance, it is necessary that the bundle of tubes does not increase in cross-sectional area due to permanent bowin so that the unit cannot be removed and replaced through the opening 5 which is necessarily of limited area, and it is one of the objects of this invention to insure against this increase in cross-sectional area of the bundle of tubes.

The shell is further provided with a base support for the unit. To this end a comparatively short longitudinally extending track 23 is welded to the bottom of the shell interiorly thereof adjacent the center. This track serves both as a guide and as a support for a part of the tube control, as will later more fully appear. It, is contracted at its forward end 24 as shown in Fig. 3, to serve as a finder. The base support further includes a track 25 at each side of and spaced from the track 23 and extending longitudinally of the shell. The tracks 25 extend from the opening e rearwardly to the header 2. The tracks 25 are welded to spaced brackets 26 which are in turn welded to the bottom of the. shell interiorly thereof. Thetracks 25 are for supporting the unit in a manner later to be described, and for facilitating removal of the unit from the shell and replacement therein.

The structure 1 further includes a transversely disposed pair of aligned substantially semicircular vertical plates 21'. There is a substantially similar pair of plates 28 at each side of and longitudinally spaced from the pair of plates 21. The tubes 8 are staggered and arranged in horizontal rows. All but the two lowermost rows open into the compartment 19, and the two lowermost rows, which are spaced from the upper rows, open into the compartment 2|. The plates have orifices 29 arranged similarly to the arrangement of the tubes and through which the tubes freely extend.

The plates 27 are disposed at the longitudinal center of the tubes and each pair of plates 28 is disposed midway between the plates 2? and the adjacent tube sheet. There is a plate 21 and a plate 28 on each side thereof for each of the groups of tubes 9 and 19. The plates support the tubes and to this end each of the plates 27 is provided with a leg 38, and each of the plates 28 is provided with a leg 3|. The legs rest upon the tracks in sliding relation therewith whereby the unit may be drawn along the tracks for removal and replacement thereof as aforesaid.

The plates are fastened to the tube sheets by tie rods in the following manner: Referring more particularly to Figs. 3 and 4, each plate 28 at the right of the plates 27 is tied to the tube sheet 15 by two spaced upper and two spaced lower rods 32. The rods are threaded into the tube sheet 15, extend through the respective plates 28 and are secured thereto by nuts 33 at each side of the plate through which the rod passes.

Each of the plates 27 and the aligned plate 28 to the left thereof are tied to the tube sheet II by two spaced upper and two spaced lower rods 34. The rods are threaded into the tube sheet l I, extend through the respective plates 28 at the left and the respective plates 2'1 and are secured thereto by nuts 35 at each side of the respective plates 28 and 21 through which the rod passes.

The plates 27 are not tied to the plates 28 at the right thereof. This is to permit the free bowing of the tubes as will presently appear. The plates 28 at the right of the plates 21 are thus held in fixed relation to the tube sheet [5, and the plates 21 and the plates 28 to the left thereof are held in fixed relation to each other and to the tube sheet ll, that is to say the respective plates are held against movement longitudinally of the tubes relative to their respective tube sheets.

The plates of each pair have vertical adjacent inner edges 36 and opposite outer substantially semi-circular edges 31. Each of the plates has upper and lower inclined corners 38 at the ends on its edge 36 providing on each pair of plates a top and bottom V-shaped groove 39. The plates 28 have straight horizontal upper edges 40 extending from their respective corners 38 to their respective outer semi-circular edges 3?. The plates 28 have straight horizontal lower edges 4| extending from their respective corners 38 to their respective legs 3!. The plates 2'! are formed somewhat differently than the plates 28. The plates 2'! at their upper and lower ends, and adjacent their corners 38, have shoulders 42, each shoulder having a horizontal wall 43 and a vertical abutment wall 44.

The tubes of each group 9 and Ill, when bowed, are bowed laterally outward, and the respective plates moved therewith laterally outward correspondingly, the plates of each pair, during such bowing, spreading apart along their vertical inner edges 36. The tubes are preferably straight tubes as shown, and will be so considered.

The control instrumental in efiecting the bowing of the tubes is composed of two separate means or devices. One of the means or devices is for bowing the tubes when under thermal expansion, and is indicated generally by the reference numeral 45. The other means or device is to insure the tubes being restored to their normal condition when under thermal contraction, and is indicated generally by the reference numeral 46.

The device generally indicated as 45, includes four tube-bowing members 4?, one at the top and one at the bottom of each of the tube groups 9 and 18. Each of the members 41 is secured to the tube sheets H and I5, and is bent inwardly to form an angle 48 at its center, that is to say at its correlated plate 21. It seats in its correlated shoulder 42 and bears against the abutment wall 44 of the shoulder at the angle. It is adjacent to its correlated edge 40 or 4|, as the case may be, of the plates 28.

Each member 47 includes a bar 49 rectangular in cross section and containing the angle 48. The bar is secured at its rear end, as by welding or otherwise, to the tube sheet I I, and is secured at its forward end to a turnbuckle 50.

The turnbuckle is best shown in Fig. 5 and includes a forked rod 5| in which fork the forward end of the bar 49 is fitted and welded. The rod 5i at its opposite end is provided with a head 52. The turnbuckle further includes a threaded rod 53 which is screwed at its forward end in the tube sheet and a member 54 which is made in two pieces 55 and 56 welded together, the piece 55 having a threaded bore 51 screwed onto the threaded rod 53 at its rear end. The other piece 56 is bored to provide a shoulder 58. The rod 5| extends into the bore with the head 52 seated against the shoulder 58. By turning the member 54 the tube-bowing member 41 may be tensioned to the extent desired.

It is intended that the descaling take place during the normal operation of the heat exchanger, but if desired, fluid of a higher temperature than that used for the normal operation may be periodically supplied through the inlet alternately with a supply of cold fluid into the shell through an inlet 3 to provide an independent quick method for bowing and unbowing the tubes for descaling them.

The device 45 operates as follows: As the tubes expand, the header I2 is forced rearwardly which movement causes the four tube-bowing mem bers 4! to start to straighten. Their angles 48, being in engagement with their respective abutment walls 44, simultaneously, during straightening, force each plate 21 laterally outward thereby causing the tubes of each group 9 and Ill to bow laterally outward due to their connection with these plates 21. The plates 28 follow the tubes during their bowing.

This forced bowing of the tubes continues until the tube sh et H and header l2 are stopped in their rearward movement. This may be accomplished in several ways, for instance by having an abutment (not shown) fixed to the shell at the rear of the header [2. The header in this way may be stopped before the members 4? are completely straight.

However in the present instance the members 47 are relied upon for stopping the aforesaid rearward movement, and this is effected upon the members 4? becoming straight. After this any further tube expansion that might occur causes automatic further bowing of the tubes during which further bowing the abutment walls 64 move laterally outward away from engagement with their respective angles 48.

During contraction of the tubes the reverse operations take place in an obvious manner. The tubes begin to unbow and if the abutment walls is have separated from their respective members 4'! the unbowing continues until the abutment walls M engage their respective members 41. Thereafter further contraction of the tubes causes the further unbowing and causes the abutment walls 44 to force their respective members i! inward, bending the members 42' to form the angles 48.

During these unbowing operations the header [2, the tube sheet l and the adjacent tube ends move forwardly to their original positions. The

device and its operation is similar to that of the before mentioned patent. However, as aforesaid, at times the unbowing to return the tubes to their original condition is not completed and instead, after the tubes have prematurely stopped unbowing, further contraction thereof results in moving the header I2, tube sheet H and adjacent tube ends further forwardly past their normal positions with the disadvantages following that have already been mentioned.

It is the object of this invention to prevent this and to insure the intended unbowing of the tubes. The device 56, best shown in detail in Fig. 4, accomplishes this. It includes two telescopic members 59, extending longitudinally parallel to the tubes between the tube sheets ii and 15. The members 59 aredisposed one above the other in the central Vertical plane or" the bundle of tubes, the top member 59 extending into the top V-shaped grooves 3i and the bottom member 59 extending into the bottom V sh'aped grooves 39. The top member 59 is disposed between the top tubebowing members al above the tubes, and the bottom member 59 is disposed between the bottom tube-bowing members fill below the tubes.

Each member as includes a long tube til secured at One end, as by welding, indicated at eta,

to one of the tube sheets, in the present instance the tube sheet l5, and a short tube 6! extending into the opposite end of the tube as in sliding relation therewith. Tube 65 is secured, as by welding, indicated at 6%, at its outer end to the tube sheet H.

The track 23 is disposed forwardly of the piates 22 and the tubes 69 are secured together by a plate 62 disposed above the tract: 25.- andextending longitudinally between the tube groups 9 and 3. The plate 52 is secured to the tubes as by welding, as indicated at 65c, and serves to prevent the members 59 from bending, and further supports the top member 59 from the bottom member 59.

A post 63 is secured to the lower tube fall, as

by weiding. The. post is in line with the track 23 and includes two side plates as extending from the lower tube 63 downwardly to and overlapping the sides of the track 23 and a cross plate 65 which rests upon the track 23 thus supporting the bottom member 59-. When the unit is r moved from the shell the plate 85 merely slides along the track 23 Lmtil it is free thereof. When the unit is replaced the plate meets and rides upon the track 23, the contracted end is of the track assisting the plate 65 in finding the track 23 if found necessary. 7

The tubes are of a length equal to the distance between the tube sheets i! and 15 when in their normal relative positions so that their telescoped ends which are adjacent the tubes 6| abut the tube sheet H when it is in its normal position.

The operation of the device 46 is simple. When tubes 8 expand thermally, tube sheet H, header l2, and the short tubes 6! move rearwardly as a unit away from the tubes 56 which, as previously explained, are anchored to tube sheet lb. The longitudinal separation of tube sheet l I from the tubes 59 is illustrated in Fig. 10 although the amount thereof has been exaggerated for purposes of illustration. The extent of such separation will be limited by device 55 when members 4! have reached straight positions. Upon thermal contraction of tubes 2, tube sheet H, header l2, and the short tubes 6! move forwardly as a unit toward the tubes 58, and tubes i telescope into tubes 58. When tube sheet ii encounters tubes St, the latter will function to stop any further forward movement of the former. If tubes 8 are still in bowed con: dition when sheet i l is stopped by tubes 69, they will still continue to contract to a straight condition. Upon reaching such a straight condi tion, however, the tubes will be prevented from contracting any further and of course there will be no further bowing.

While there has been hereinbefore described an approved embodiment of this invention, it will be understood that many and various changes and modifications in form, arrangement of parts and details of construction thereof may be made without departing from the spirit of the invention and that all such changes and modifications as fall within the scope of the appended claims are contemplated as part of this invention.

The invention claimed and desired to be secured by Letters Patent is:

1. In combination, a structure for a heat exchanger comprising a bundle of heat exchange tubes arranged in two groups and means at the opposite ends of said bundle holding said tubes together and providing inlets and outlets therefor, said structure being free to float at at least one end thereof adapting said structure for relative outward and return inward movements of the ends thereof, from and to their relative normal positions, when said tubes are under thermal expansion and contraction respectively; and a control for effecting descaling of said tubes, including a tie rod extending longitudinall of each of said groups of tubes between said structure ends and connected at its ends to the adjacent ends of said structure and bearing against an intermediate portion of its correlated group of tubes, each of said tie rods being normally bowed before expansion of said tubes for effecting bowing of said tubes by lateral pressure against said intermediate portions due to straightening of said tie rods during expansion of said tubes, said control further including a telescopic bar-like member secured at its ends to the adjacent ends of said structure and having limited telescopic retractable movement for checking said structure ends inward movement due to contraction of said tubes when at said normal positions whereby further contraction will insure said tubes unbowing to their normal positions.

2. In combination, a structure for a heat exchanger comprising a bundle of heat exchange tubes arranged in two groups and means at the opposite ends of said bundle holding said tubes together and providing inlets and outlets there for, said structure being free to boat at at least one end thereof adapting said structure for relative outward and return inward movements of the ends thereof, from and to their relative normal positions, when said tubes are under thermal expansion and contraction respectively; and a control for effecting descalin of said tubes, including a tie rod extending longitudinally of each of said groups of tubes between said structure ends and connected at its ends to the adjacent ends of said structure and bearing against an intermediate portion of its correlated group of tubes, each of said tie rods being normally bowed before expansion of said tubes for effecting bowing of said tubes by lateral pressure against said intermediate portions due to straightening of said tie rods during expansion of said tubes, said control further including two parallel bar-like members spaced on opposite sides of the axis of said structure for spacing said structure ends at said normal positions and for checking said structure ends inward movement due to contraction of said tubes when at said normal positions whereby further contraction will insure said tubes unbowing to their normal positions, and a tie member secured at its opposite ends to said bar-like members between the ends thereof, said tie member preventing bending of said bar-like members.

3. In combination, a structure for a heat exchanger comprising a bundle of heat exchange tubes arranged in two groups and means at the opposite ends of said bundle holding said tubes together and providing inlets and outlets therefor, said structure being free to float at at least one end thereof adapting said structure for relative outward and return inward movements of the ends thereof, from and to their relative normal positions, when said tubes are under thermal expansion and contraction respectively; and a control for efiecting descaling of said tubes, including a tie rod extending longitudinally of each of said groups of tubes between said structure ends and connected at its ends to the adjacent ends of said structure and bearing against an intermediate portion of its correlated roup of tubes, each of said tie rods bein normally bowed before expansion of said tubes for effecting bowing of said tubes by lateral pressure against said intermediate portions due to straightening of said tie rods during expansion of said tubes, said control further including two parallel telescopic barlike members spaced on opposite sides of the axis of said structure for spacing said structure ends at said normal positions each member being secured at its outer end to the adjacent end of said structure and having limited telescopic retractable movement for checking said structure ends inward movement due to contraction of said tubes when at said normal positions whereby further contraction will insure said tubes unbowing to their normal positions.

4. In combination, a structure for a heat exchanger comprising a bundle of heat exchange tubes arranged in two groups and means at the opposite ends of said bundle holding said tubes together and providin inlets and outlets therefor, said structure being free to float at at least one end thereof adapting said structure for relative outward and return inward movements of the ends thereof, from and to their relative normal positions, when said tubes are under thermal expansion and contraction respectively; and a control for effecting descaling of said tubes, including a tie rod extending longitudinally of each of said groups of tubes between said structure ends and connected at its ends to the adjacent ends of said structure and bearing against an intermediate portion of its correlated group of tubes, each of said tie rods being normally bowed before expansion of said tubes for effecting bowing of said tubes by lateral pressure against said intermediate portions due to straightening of said tie rods during expansion of said tubes, said control further including two parallel telescopic barlike members spaced on opposite sides of the axis of said structure for spacing said structure ends at said normal positions each member being secured at its outer end to the adjacent end of said structure and having limited telescopic retractable movement for checking said structure ends inward movement due to contraction of said tubes when at said normal positions whereby further contraction will insure'said tubes unbowing to their normal positions, and a tie member secured at its opposite ends to said bar-like members between the ends thereof, said tie member preventing bending of said bar-like members.

5. In a heat exchanger having a shell, a tube sheet fixedly secured thereto, a tube bundle, and a floating tube sheet, control apparatus to descale the tubes comprising a pair of tie rods each secured to the tube sheets at its opposite ends, said tie rods being bent inwardly toward each other to form angles and being adapted to straighten under tension, a pair of plates disposed inter.- mediate the tube sheets and orificed for the reception of the tubes, abutment means on each plate arranged opposite the adjacent tierod angular portion, said abutment means being adapted to transmit lateral movement from the tie rod to the tubes to bend the same as the tie rods straighten out in response to tension caused by the movement of the floating tube sheet upon thermal expansion of the tubes, and a stop device to prevent the floating tube sheet from moving back beyond normal position under thermal contraction of the tube sheets thereby to insure the tubes unbowing to their normal position, such stop device including a first element rigidly secured to the fixedly secured tube sheet in abutting relation to the floating tube sheet in the normal position of the latter, and a second element rigidly secured to the floating tube sheet and arranged in telescopic relation to the first element.

6. In a heat exchanger having a shell, a tube sheet fixedly secured thereto, a tube bundle, and a floating tube sheet, control apparatus to descale the tubes comprising a pair of tie rods each secured to the tube sheets at its opposite ends, said tie rods being bent inwardly towards each other to form angles and being adapted to straighten under tension, a pair of plates disposed intermediate the tube sheets and orificed for the reception of the tubes, abutment means on the plates arranged to receive the tie rods at their angular portions, and a telescopic bar-like member disposed longitudinally of the tubes between the tube sheets and secured at its opposite ends to said tube sheets, the arrangement of the tie rods being such that they will straighten out under tension as the floating tube sheet moves away from the fixedly secured tube sheet under thermal expansion thereby forcing the pair of plates apart thereby to cause the tubes to bend, and the 10 arrangement of the bar-like member being such that upon the return movement of the floating tube sheet upon thermal contraction such member will function to stop such return movement of the floating tube sheet at normal position thereby to insure the tubes unbowing to their normal positions.

7. In a heat exchanger having a shell, a tube sheet fixedly secured thereto, a tube bundle, and a floating tube sheet, controlapparatus to descale the tubes comprising a pair of tie rods extending longitudinally of said tubes, each of such rods being secured to the tube sheets at its opposite ends and being bent inwardly toward each other to form angles whose apices are opposite each other, a pair of plates disposed intermediate the tube sheets and orificed for the reception of the tubes, a shoulder on the inner side of each plate arranged to abut the adjacent tie rod at its angular portion, and a telescopic member disposed longitudinally of the tubes between the tube sheets, one element of such member being attached to the floating tube sheet and the other member being attached to the fixedly secured tube sheet, the arrangement of the tie rods being such that they will straighten out under tension as the floating tube sheet moves away from the secured tube sheet under thermal expansion and engage the shoulders of the plates to force such plates apart thereby to cause the tubes to bend, and the arrangement of telescopic member being such that upon the return movement of the floating tube sheet upon thermal contraction such telescopic member will close to form a stop for the return movement of the floating tube sheet at normal position thereby to insure the tubes unbowing to their normal straight positions.

GEORGE B. FARKAS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,617,081 Price Feb. 8, 1927 1,716,947 Boardman June 11, 1929 1,855,552 Jacocks et a1 Apr. 26, 1932 1,953,500 Price Apr. 3, 1934 50 1,962,909 Price June 12, 1934 2,176,406 McCullough Oct, 17, 1939 

